Interbody device with opening to allow packing graft and other biologics

ABSTRACT

An intervertebral fusion device having a cage having an opening or window in its front wall that allows for the insertion of bone graft therethrough after the cage has been placed into the disc space. The device further has a faceplate that covers the front wall of the cage and provides features for securing bone screws to the adjacent vertebral bodies.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.13/673,061 filed Nov. 9, 2012, the disclosure of which is herebyincorporated by reference as if set forth in its entirety herein.

BACKGROUND OF THE INVENTION

The natural intervertebral disc contains a jelly-like nucleus pulposussurrounded by a fibrous annulus fibrosus. Under an axial load, thenucleus pulposus compresses and radially transfers that load to theannulus fibrosus. The laminated nature of the annulus fibrosus providesit with a high tensile strength and so allows it to expand radially inresponse to this transferred load.

In a healthy intervertebral disc, cells within the nucleus pulposusproduce an extracellular matrix (ECM) containing a high percentage ofproteoglycans. These proteoglycans contain sulfated functional groupsthat retain water, thereby providing the nucleus pulposus within itscushioning qualities. These nucleus pulposus cells may also secretesmall amounts of cytokines such as interleukin-1β and TNF-α as well asmatrix metalloproteinases (“MMPs”). These cytokines and MMPs helpregulate the metabolism of the nucleus pulposus cells.

In some instances of disc degeneration disease (DDD), gradualdegeneration of the intervetebral disc is caused by mechanicalinstabilities in other portions of the spine. In these instances,increased loads and pressures on the nucleus pulposus cause the cellswithin the disc (or invading macrophases) to emit larger than normalamounts of the above-mentioned cytokines. In other instances of DDD,genetic factors or apoptosis can also cause the cells within the nucleuspulposus to emit toxic amounts of these cytokines and MMPs. In someinstances, the pumping action of the disc may malfunction (due to, forexample, a decrease in the proteoglycan concentration within the nucleuspulposus), thereby retarding the flow of nutrients into the disc as wellas the flow of waste products out of the disc. This reduced capacity toeliminate waste may result in the accumulation of high levels of toxinsthat may cause nerve irritation and pain.

As DDD progresses, toxic levels of the cytokines and MMPs present in thenucleus pulposus begin to degrade the extracellular matrix, inparticular, the MMPs (as mediated by the cytokines) begin cleaving thewater-retaining portions of the proteoglycans, thereby reducing itswater-retaining capabilities. This degradation leads to a less flexiblenucleus pulposus, and so changes the loading pattern within the disc,thereby possibly causing delamination of the annulus fibrosus. Thesechanges cause more mechanical instability, thereby causing the cells toemit even more cytokines, thereby upregulating MMPs. As this destructivecascade continues and DDD further progresses, the disc begins to bulge(“a herniated disc”), and then ultimately ruptures, causing the nucleuspulposus to contact the spinal cord and produce pain.

One proposed method of managing these problems is to remove theproblematic disc and replace it with a porous device that restores discheight and allows for bone growth therethrough for the fusion of theadjacent vertebrae. These devices are commonly called “fusion devices”.

U.S. Pat. No. 6,432,106 (Fraser) discloses a fusion cage having ananterior threaded insertion hole and a face plate that covers this hole.The cavity of the Fraser cage comprises three vertical throughholes,with only the central vertical throughhole connecting to the anteriorinsertion hole.

SUMMARY OF THE INVENTION

The present invention relates to an intervertebral fusion device havinga cage having an opening or window in its front wall that allows for theinsertion of bone graft therethrough after the cage has been placed intothe disc space. Because the cage has a single vertical through hole thatconnects to that window, graft may be placed through the window so as tofill the entire cavity of the cage. The device further has a faceplatethat covers the front wall of the cage, thereby covering the windowafter the graft has been inserted. The function of the faceplate is toprovide a template for screwholes that allow the cage to be securelyfixed to the vertebral body.

Therefore, the present invention is advantageous in that it allows notonly the insertion of bone graft (through the window) after implantplacement, it also allows for its securement to adjacent vertebralbodies (via screws that pass through the faceplate).

Therefore, in accordance with the present invention, there is providedan intervertebral fusion device comprising;

-   -   a) a cage comprising a front wall having a first window        therethrough, a back wall, and two side walls connecting the        front and back walls, the front wall extending continuously        between the two side walls, the four walls defining a perimeter        and a single vertical throughhole, and    -   b) a face plate received in the window and substantially        covering the first window.        -   Also in accordance with the present invention, there is            provided a method comprising:        -   a) implanting the cage of the present invention into an            intervertebral disc space,        -   b) inserting bone graft material through the first window of            the implanted cage and into the vertical throughhole of the            cage, and        -   c) inserting a face plate into the window of the front wall            of the implanted cage to substantially cover the first            window of the cage.

DESCRIPTION OF THE FIGURES

FIG. 1A discloses a cage of the present invention without a faceplate.

FIG. 1B shows the cage of FIG. 1a having a faceplate attached thereto.

FIG. 1C discloses an exploded version of FIG. 1 b.

FIG. 1D discloses a cage of the present invention having a moveablefaceplate.

FIG. 2A shows a second combination of the cage having a faceplateattached therethrough.

FIG. 2B shows an exploded version of FIG. 2 a.

FIG. 2C discloses a non-circular washer.

FIG. 3 discloses a bone screw mating with the face plate to produce anangle α of between about 15 and 75 degrees.

DETAILED DESCRIPTION OF THE INVENTION

For the purpose of the present invention, a “front wall” includes astrur connecting the two side walls, but does not include the frontfaces of two unconnected sidewalls.

Now referring to FIGS. 1A-1C, there is provided an intervertebral fusiondevice comprising;

-   -   a) a cage 1 comprising a front wall 3 having a first window 5        therethrough, a back wall 7, and two side walls 9 connecting the        front and back walls, the front wall extending continuously        between the two side walls, the four walls defining a perimeter        and a single vertical throughhole 11, and    -   b) a face plate 21 received in the window, attached to the front        wall and substantially covering the first window.

FIG. 1A shows the cage without a faceplate. In this condition, graftmaterial can be packed or injected through the window. FIG. 1B shows thecombination of the cage having a faceplate attached therethrough. Bonescrews (not shown) may be received in the pair of screwholes 23 of thefaceplate in order to secure the device to the adjacent vertebralbodies, thereby preventing migration.

The device of the present invention can be suited for insertion into thecervical, thoracic or lumbar disc space. The particular device shown inFIG. 1A is best suited for insertion into the cervical disc spacethrough an anterior approach. The perimeter of the cage of FIG. 1Asubstantially has the shape of a cervical disc space. In someembodiments, the cervical cage has a length (L) and width (W) such thatthe length is between about 50% and 150% of the width, more preferablybetween about 80% and 120% of the width. Preferably, the cage has teeth13 extending from the upper 15 and lower 17 surfaces of the cage.

Now referring to FIG. 1D, in some embodiments, the peripheries of thefaceplate and window having mating features that allow the faceplate tobe inserted into the window, and then slightly shifted so that it cannotback out. IN FIG. 1d , the faceplate has a length that is shorter thanthe corresponding window 5. The periphery of the faceplate has notches53 that correspond to the protrusions 51 on the periphery of the window.These mating features allow the faceplate to be inserted into the windowand past the protrusions. Once, the faceplate so inserted shifts (due toits shorter length), the faceplate may no longer easily be removed fromthe window.

Also as shown in FIG. 2A-2B, in some embodiments, the face plate has ahorizontal slot 25 extending therethrough, with first 27 and second 29washers received in the slot. The function of the washers is to receivefirst and second bone screws (not shown) that allow for fixation of thecage. The washers are adapted to be slidable in the slot, so that theirpositions may be infinitely adjusted to suit the desires of the surgeon.In some embodiments, as in FIG. 2C, at least one (and preferably both)of the washers 31 have a cam shape. This cam shape may provide to thewasher a first dimension D1 and a second dimension D2, wherein D1 isgreater than D2. This non-circular shape allows the washer to be firstslid to an appropriate location within the slot and then turned 90degrees in order to lock that position. In some embodiments, the washermay have a threaded receiving hole.

In some embodiments (not shown), the there may be three washers disposedin the slot, whereby the two outer washers receive bone fixation means(such as a bone screw) pointing in one direction and the middle washerreceives a bone fixation means in the other direction.

In some embodiments (not shown), the there may be four washers disposedin the slot, whereby a first two alternating washers receive bonefixation means (such as a bone screw) pointing in one direction and theremaining two washers each receive a bone fixation means in the otherdirection.

Now referring to FIG. 2B, in some embodiments, the device comprisesfirst and second screwholes, each screwhole adapted to receive a bonescrew. In some of these embodiments, each screwhole is formed in boththe plate and the cage. As in FIG. 2B, in some embodiments, eachscrewhole is at least partially open. In these open embodiments, thefront wall comprises a top surface 41 and a bottom surface, wherein aportion 43 of the first screwhole formed in the cage opens at leastpartially onto the top surface of the cage, and wherein a portion of thesecond screwhole formed in the cage opens at least partially onto thebottom surface of the cage. The open nature of these allows for the useof larger bone screws within the same cage, thereby enhancing thefixation strength of the device. Lastly, there are preferably first andsecond bone screws (not shown) respectively received in the first andsecond screwholes.

In some embodiments, the front wall has a front surface, the face platehas a front surface, and the front surfaces are substantially co-planar.This produces the desirable zero-profile shape that reduces the chancesof irritation of the great vessels that sit anterior to the device inthe cervical spine.

In some embodiments, and now referring to FIG. 3, each bone screw 51preferably mates with the face plate and cage to produce an angle α ofbetween about 15 and 75 degrees.

The faceplate may be attached to the anterior wall of the cage by anyconventional means. In some embodiments, the face plate is attached tothe front wall by a hinge. In others, the faceplate forms a Morse taperwith the window and is attached to the front wall by a press fitmechanism, thereby locking the faceplate in place.

The intervertebral fusion cage of the present invention may bemanufactured from any biocompatible flexible material suitable for usein interbody fusion procedures. In some embodiments, the cage comprisesa composite comprising 40-100% polyarylethyl ketone PAEK, and optionally1-60% carbon fiber. Such a cage is radiolucent. Preferably, thepolyarylethyl ketone PAEK is selected from the group consisting ofpolyetherether ketone PEEK, polyether ketone ketone PEKK, polyetherketone ether ketone ketone PEKEKK, and polyether ketone PEK. Preferably,cage is made from woven, long carbon fiber laminates. Preferably, thePAEK and carbon fiber are homogeneously mixed. In some embodiments, thecomposite consists essentially of PAEK and carbon fiber. In someembodiments, the composite comprises 60-80 wt % PAEK and 20-40 wt %carbon fiber, more preferably 65-75 wt % PAEK and 25-35 wt % carbonfiber. In some embodiments, the cage is made from materials used incarbon fibers cages marketed by DePuy Spine, Raynham, Mass., USA. Insome embodiments, the composite is PEEK-OPTIMA™, available from Invibioof Greenville, N.C.

Typically, each of the faceplate and washer is made from a biocompatiblemetal in order to enhance the strength of the screw-receiving component.In some embodiments, the faceplate is made from a material selected fromthe group consisting of stainless steel, chromium-cobalt and a titaniumalloy.

Typically, each screw is made from a biocompatible metal selected fromthe group consisting of stainless steel, chromium-cobalt and a titaniumalloy.

In some embodiments, a screw is used disclosed as the fixation means forfixing the cage to the vertebral bodies. However, any conventionalfixation means for fixing a cage to a vertebral body can be used.

In some embodiments, the fusion cage of the present invention is used totreat DDD and is placed within a disc space between adjacent vertebralbodies. In others, it is used in a corpectomy case, and replaces avertebral body.

In some embodiments, after the cage of the present invention has beeninserted into the disc space, the surgeon may place an endplatepreparation instrument (such as a curette) through the anterior windowof the cage and prepare the portion of the endplate not supported bybone. This method insures that not only is the endplate adequatelyprepared, but there remains an intact rim of cortical bone supportingthe endplate.

In some embodiments, the device further comprises graft materialdisposed within the vertical throughole of the cage. In theseembodiments, the graft is inserted by a method comprising:

-   -   a) implanting the cage of the present invention into an        intervertebral disc space,    -   b) inserting bone graft material through the first window of the        implanted cage and into the vertical throughhole of the cage,        and    -   c) attaching a face plate to the front wall of the implanted        cage to substantially cover the first window of the cage.

In some embodiments, the bone graft material is injected through thefirst window. In some embodiments, this bone graft material is flowable.In some embodiments, the flowable graft material may be HEALOS FX™, aflowable collagen-based material available from DePuy Spine of Raynham,Mass., USA.

In other embodiments, the bone graft material is packed into thevertical throughhole.

In some embodiments, the grail material may comprises a bone formingagent. In some embodiments, the bone forming agent is a growth factor.As used herein, the term “growth factor” encompasses any cellularproduct that modulates the growth or differentiation of other cells,particularly connective tissue progenitor cells. The growth factors thatmay be used in accordance with the present invention include, but arenot limited to, members of the fibroblast growth factor family,including acidic and basic fibroblast growth factor (FGF-1 and FGF-2)and FGF-4; members of the platelet-derived growth factor (PDGF) family,including PDGF-AB, PDGF-BB and PDGF-AA; EGFs; VEGF; members of theinsulin-like growth factor (IGF) family, including IGF-I and -II; theTGF-β superfamily, including TGF-β1, 2 and 3; osteoid-inducing factor(OIF), angiogenin(s); endothelins; hepatocyte growth factor andkeratinocyte growth factor; members of the bone morphogenetic proteins(BMPs) BMP-1, BMP-3, BMP-2, OP-1, BMP-2A, BMP-2B, BMP-7 and MP-14,including HBGF-1 and HBGF-2; growth differentiation factors (GDFs),members of the hedgehog family of proteins, including indian, sonic anddesert hedgehog; ADMP-1; bone-forming members of the interleukin (IL)family; rhGDF-5; and members of the colony-stimulating factor (CSF)family, including CSF-1, G-CSF, and GM-CSF; and isoforms thereof.

In some embodiments, platelet concentrate is provided as the boneforming agent. In one embodiment, the growth factors released by theplatelets are present in an amount at least two-fold (e.g., four-fold)greater than the amount found in the blood from which the platelets weretaken. In some embodiments, the platelet concentrate is autologous. Insome embodiments, the platelet concentrate is platelet rich plasma(PRP). PRP is advantageous because it contains growth factors that canrestimulate the growth of the bone, and because its fibrin matrixprovides a suitable scaffold for new tissue growth.

In some embodiments, the bone forming agent comprises an effectiveamount of a bone morphogenic protein (BMP). BMPs beneficially increasingbone formation by promoting the differentiation of mesenchymal stemcells (MSC) into osteoblasts and their proliferation.

In some embodiments, between about 1 ng and about 10 mg of BMP areadministered into the target disc space. In some embodiments, betweenabout 1 microgram (μg) and about 1 mg of BMP are administered into thetarget disc space.

In many preferred embodiments, the bone forming agent is a porousmatrix, and is preferably injectable.

The porous matrix of the present invention may contain porous orsemi-porous collagen, extracellular matrices, metals (such as Ti, Ti64,CoCr, and stainless steel), polymers (such as PEEK, polyethylene,polypropylene, and PET) resorbable polymers (such as PLA, PDA, PEO, PEG,PVA, and capralactides), bone substitutes (such as TCP, HA, and CaP),autograft, allograft, xenograft, and/or blends thereof. Matrices may beorientated to enable flow from bony attachment locations to theaspiration port. Matrices may be layered with varying densities, porestructures, materials to enable increase stem filter at desiredlocations via density, pore size, affinity, as well as fluid flowcontrol (laminar, turbilant, and/or tortuous path).

In some embodiments, the porous matrix is a mineral. In one embodiment,this mineral comprises calcium and phosphorus. In some embodiments, themineral is selected from the group consisting of calcium phosphate,tricalcium phosphate and hydroxyapatite. In one embodiment, the averageporosity of the matrix is between about 20 and about 500 μm, forexample, between about 50 and about 250 μm. In yet other embodiments ofthe present invention, in situ porosity is produced in the injectedmatrix to produce a porous scaffold in the interbody space. Once the insitu porosity is produced in the space, the surgeon can inject othertherapeutic compounds into the porosity, thereby treating thesurrounding tissues and enhancing the remodeling process of the targettissue.

In some embodiments, the mineral is administered in a granule form. Itis believed that the administration of granular minerals promotes theformation of the bone growth around the minerals such thatosteointegration occurs.

In some embodiments, the mineral is administered in a settable-pasteform. In this condition, the paste sets up in vivo, and therebyimmediately imparts post-treatment mechanical support to the interbodyspace.

In another embodiment, the treatment is delivered via injectableabsorbable or non-absorbable cement to the target space. The treatmentis formulated using bioabsorbable macro-sphere technologies, such thatit will allow the release of the bone forming agent. The cement willprovide the initial stability required to treat pain in target tissues.These tissues include, but are not limited to, hips, knee, vertebralbody and iliac crest. In some embodiments, the cement is selected fromthe group consisting of calcium phosphate, tricalcium phosphate andhydroxyapatite. In other embodiments, the cement is any hardbiocompatible cement, including PMMA, processed autogenous and allograftbone. Hydroxylapatite is a preferred cement because of its strength andbiological profile. Tricalcium phosphate may also be used alone or incombination with hydroxylapatite, particularly if some degree ofresorption is desired in the cement.

In some embodiments, the porous matrix comprises a resorbable polymericmaterial.

In some embodiments, the bone forming agent comprises an injectableprecursor fluid that produces the in situ formation of a mineralizedcollagen composite. In some embodiments, the injectable precursor fluidcomprises:

-   -   a) a first formulation comprising an acid-soluble type I        collagen solution (preferably between about 1 mg/ml and about 7        mg/ml collagen) and    -   b) a second formulation comprising liposomes containing calcium        and phosphate.

Combining the acid-soluble collagen solution with the calcium- andphosphate-loaded liposomes results in a liposome/collagen precursorfluid, which, when heated from room temperature to 37° C., forms amineralized collagen gel.

In some embodiments, the liposomes are loaded withdipalmitoylphosphatidylcholine (90 mol %) and dimyristoylphosphatidylcholine (10 mol %). These liposomes are stable at roomtemperature but form calcium phosphate mineral when heated above 35° C.,a consequence of the release of entrapped salts at the lipid chainmelting transition. One such technology is disclosed in Pederson,Biomaterials 24: 4881-4890 (2003), the specification of which isincorporated herein by reference in its entirety.

Alternatively, the in situ mineralization of collagen could be achievedby an increase in temperature achieved by other types of reactionsincluding, but not limited to, chemical, enzymatic, magnetic, electric,photo- or nuclear. Suitable sources thereof include light, chemicalreaction, enzymatically controlled reaction and an electric wireembedded in the material. To further elucidate the electric wireapproach, a wire can first be embedded in the space, healed to createthe calcium deposition, and then withdrawn. In some embodiments, thiswire may be a shape memory such as nitinol that can form the shape.Alternatively, an electrically-conducting polymer can be selected as thetemperature raising element. This polymer is heated to form thecollagen, and is then subject to disintegration and resorption in situ,thereby providing space adjacent the mineralized collagen for the boneto form.

In some embodiments, the osteoconductive material comprises calcium andphosphorus. In some embodiments, the osteoconductive material compriseshydroxyapatite. In some embodiments, the osteoconductive materialcomprises collagen. In some embodiments, the osteoconductive material isin a particulate form.

Specific matrices may be incorporated into the device to provide loadbearing qualities, enable directional bone formation, and/or controldensity of regenerated bone (cortical vs cancellous) or enable cellformation for soft tissue attachment. Nanotubes or nanocrystals can beorientated in a generally axial direction to provide for load bearingabilities as well as capillary wicking of vascular flow to furtherenhance directional bone formation. Biocompatible nanotubes cancurrently be produced from either carbon or titanium or hone substitutesincluding Ca, HA, and TCP.

In one embodiment, the bone forming agent is a plurality of viable exvivo osteoprogenitor cells. Such viable cells, introduced into theinterbody space, have the capability of at least partially supplementingthe in situ drawn stem cells in the generation of new bone for theinterbody space.

In some embodiments, these cells are obtained from another humanindividual (allograft), while in other embodiments, the cells areobtained from the same individual (autograft). In some embodiments, thecells are taken from bone tissue, while in others, the cells are takenfrom a non-bone tissue (and may, for example, be mesenchymal stem cells,chondrocytes or fibroblasts). In others, autograft osteocytes (such asfrom the knee, hip, shoulder, finger or ear) may be used.

In one embodiment, when viable ex vivo cells are selected as anadditional therapeutic agent or substance, the viable cells comprisemesenchymal stem cells (MSCs). MSCs provide a special advantage foradministration into the interbody space because it is believed that theycan more readily survive the relatively harsh environment present in thespace; that they have a desirable level of plasticity; and that theyhave the ability to proliferate and differentiate into the desiredcells.

In some embodiments, the mesenchymal stem cells are obtained from honemarrow, such as autologous bone marrow. In others, the mesenchymal stemcells are obtained from adipose tissue, preferably autologous adiposetissue.

In some embodiments, the mesenchymal stem cells injected into theinterbody space are provided in an unconcentrated form, e.g., from freshbone marrow. In others, they are provided in a concentrated form. Whenprovided in concentrated form, they can be uncultured. Uncultured,concentrated MSCs can be readily obtained by centrifugation, filtration,or immuno-absorption. When filtration is selected, the methods disclosedin U.S. Pat. No. 6,049,026 (“Muschler”), the specification of Which isincorporated herein by reference in its entirety, can be used. In someembodiments, the matrix used to filter and concentrate the MST's is alsoadministered into the interbody space.

In some embodiments, bone cells (which may be from either an allogeneicor an autologous source) or mesenchymal stem cells, may be geneticallymodified to produce an osteoinductive bone anabolic agent which could bechosen from the list of growth factors named herein. The production ofthese osteopromotive agents may lead to bone growth.

Recent work has shown that plasmid DNA will not elicit an inflammatoryresponse as does the use of viral vectors. Genes encoding bone(anabolic) agents such as BMP may be efficacious if injected into theuncoupled resorbing bone. In addition, overexpression of any of thegrowth factors provided herein or other agents which would limit localosteoclast activity would have positive effects on bone growth. In oneembodiment, the plasmid contains the genetic code for human TGF-β orerythropoietin (EPO).

Accordingly, in some embodiments, the additional therapeutic agent isselected from the group consisting of viable cells and plasmid DNA.

A matrix may be made from hydrogels or may incorporate a hydrogel ascomponent of the final structure. A hydrogel may be used to expand andenhance filling, improve handling characteristics or increase vacuumpressure. The increased vacuum pressure may be used to determineadequate hydration/stem cell filtration.

In all cases, excess bone marrow aspirate can be collected and mixedwith added graft extenders including collagen like the HEALOS™ andHEALOS FX™, each of which is available from DePuy Spine Inc, Raynharn,Mass., USA.

Although the present invention has been described with reference to itspreferred embodiments, those skillful in the art will recognize changesthat may be made in form and structure which do not depart from thespirit of the invention.

I claim:
 1. A method comprising the steps of: implanting a cage into an intervertebral disc space that is defined between a first vertebra and a second vertebra, such that an upper wall of the cage faces the first vertebra, and a lower wall opposite the upper wall along a vertical direction faces the second vertebra, and the cage includes 1) a front end and a back end, the front end having a front wall that defines a front surface and a rear surface that faces opposite the front surface, and 2) an aperture that extends through the front wall from the front surface to the rear surface such that the front surface defines an opening to the aperture, the opening to the aperture elongate along a horizontal plane that is perpendicular to the vertical direction, wherein the cage defines a throughhole that extends through the upper and lower walls, the throughhole configured to receive bone graft material, and the cage consists of poly-ether-ether-ketone (PEEK); threadedly mating a threaded shaft in a threaded receiving hole that extends into a receiving member, the receiving member is supported by a face plate that is supported by the cage, and the receiving member extends into a hole that extends through the face plate, and wherein the receiving member defines a front opening to the threaded receiving hole, and the method further comprises the step of inserting the threaded shaft into the aperture; and moving the front opening to the threaded receiving hole along the horizontal plane.
 2. The method of claim 1, wherein the cage defines first and second aperture ends of the aperture along the horizontal plane.
 3. The method of claim 1, wherein the cage is configured to receive an endplate preparation instrument through the aperture.
 4. The method of claim 1, wherein the receiving member comprises a washer.
 5. The method of claim 1, wherein the faceplate closes a portion less than an entirety of the aperture.
 6. The method of claim 1, wherein the moving step comprises moving the receiving member along the horizontal plane.
 7. The method of claim 6, wherein the front wall defines first and second aperture sides of the aperture, and the moving step comprises translating the face plate along the cage to a position whereby both 1) the face plate is spaced from the first aperture side in a direction toward the second aperture side with respect to a view of the cage and the face plate that is oriented in a direction from the front surface to the rear surface, and 2) the face plate is spaced from the second aperture side in a direction toward the first aperture side with respect to the view.
 8. The method of claim 1, wherein the front opening to the threaded receiving hole is not recessed in the receiving member.
 9. A method comprising the steps of: implanting a cage into an intervertebral disc space that is defined between a first vertebra and a second vertebra, such that an upper wall of the cage faces the first vertebra, and a lower wall opposite the upper wall along a vertical direction faces the second vertebra, and the cage includes 1) a front end and a back end, the front end having a front wall that defines a front surface and a rear surface that faces opposite the front surface, and 2) an aperture that extends through the front wall from the front surface to the rear surface such that the front surface defines an opening to the aperture, the opening to the aperture elongate along a horizontal plane that is perpendicular to the vertical direction; inserting bone graft material into a throughhole of the cage that extends through the upper and lower walls; threadedly mating a threaded shaft in a threaded receiving hole that extends into a receiving member, wherein the receiving member defines a front opening to the threaded receiving hole, and the implanting step further comprises inserting the threaded shaft into the aperture, wherein the receiving member is supported by a face plate that is supported by the cage, and the receiving member extends into a hole that extends through the face plate; and moving the front opening to the threaded receiving hole along the horizontal plane.
 10. The method of claim 9, wherein the receiving member comprises a washer.
 11. The method of claim 9, wherein the faceplate closes a portion less than an entirety of the aperture.
 12. The method of claim 9, wherein the moving step comprises moving the receiving member along the horizontal plane. 